1. Field of the Invention
This invention relates to medical devices with inflatable cuffs and more particularly to such devices intended for use in connection with nitrous oxide and oxygen administration.
2. Description of the Prior Art
In connection with surgical procedures, a medical device such as a tracheal tube may be employed. A tracheal tube usually includes an elongated tube adapted to be inserted through the mouth and to extend through the trachea and into communication with the lung area. Such tubes normally include an inflatable cuff positioned in the tracheal area and inflatable to engage the trachea and block the passage of fluid through the tracheal area exteriorly of the elongated tube. A smaller tube contiguous to the larger elongated tube may be provided for conducting air under suitable pressure to the cuff for inflating the cuff. The distal end of this small tube is connected to the interior of the cuff for this purpose. Alternatively, a small lumen may be formed in the wall of the elongated tube and connected to the interior of the cuff to provide a passage for air to inflate the cuff.
It is desirable that excessive pressure within the cuff be avoided because it is believed that when the pressure within the cuff exceeds the venous pressure in the capillary bed of the trachea, post-operative trauma may result.
In connection with some surgical procedures, nitrous oxide (N.sub.2 O) may be employed as an anesthetic. Present cuffs employed with such tracheal tubes are made of plasticized polyvinyl chloride. It has been found that nitrous oxide diffuses through a wall of such material at a substantially greater rate than the diffusion rate of nitrogen (N.sub.2) therethrough. (Nitrogen makes up approximately 80% of content of air.) As a result, the pressure within the cuff may rise to an undesirably high level.
In other cases, a patient may be supplied over a period of several days with an enriched air supply comprising, for example, 40% oxygen, using a tracheal tube of the type described above. When the cuff is made of conventional polyvinyl chloride material, a problem of excessive pressure within the cuff may again be encountered. Oxygen tends to diffuse through such material at a slightly higher rate than nitrogen, and hence the oxygen-enriched air supplied to the patient, which comprises 40% oxygen compared to 20% oxygen in the air supplied for inflating the cuff, tends to diffuse through the cuff from the exterior more rapidly than the air within the cuff diffuses outwardly. As a result, the pressure within the cuff may build over a period of several days to an undesirably high level.
All prior art methods known to the applicant have been directed toward mechanical means for limiting the pressure in the cuff, for example, by incorporating a pressure regulator in the air supply to the cuff to control the pressure in the cuff. These mechanical means have involved undesirable inconvenience, expense and performance compromises.
In accordance with the present invention, the cuff is made of a material which has a significantly lower diffusion rate for nitrous oxide and oxygen in relation to the diffusion rate for nitrogen, so that any pressure build-up is at a lower rate and the pressure does not reach a level which causes trauma to the trachea within the time frame of most anesthesia procedures.
It is an object of this invention to provide a medical device, such as a tracheal tube, having an inflatable cuff which is formed of a material having a lower diffusion rate for nitrous oxide and oxygen than materials presently employed for such cuffs.